1. Field of the Invention
The present invention generally relates to a display panel, and more particularly to the structure and layout of pixel unit cells of liquid crystal on silicon (LCOS) display panel.
2. Description of the Prior Art
Liquid crystal on silicon (LCOS or LCOS) is a reflective technology that can produce higher resolution image, at lower cost, than liquid crystal display (LCD), and has been developed as the optical engine for micro-projection or micro-display system. FIG. 1 shows a pixel unit cell circuit 10, which includes a metal-oxide-semiconductor (MOS) addressing transistor 12 and a pixel capacitor 14. The gate G of the MOS transistor 12 is connected to and addressed by a scan line (SCAN), and the source S of the MOS transistor 12 is connected to a data line (DATA) for receiving image data. The drain D of the MOS transistor 12 is connected to the pixel capacitor 14, which is implemented by connecting its drain, source and bulk VDDA together (or usually called MOS capacitor in the field). FIG. 2A shows the layout of a pixel block consisting of eight pixel unit cells. FIG. 2B shows an enlarged view of the layout of the pixel capacitor 14 of a pixel unit cell, and FIG. 2C shows the corresponding cross-sectional view of FIG. 2B along the line 2C-2C′. In the figures, a pixel cap bottom plate (or usually called OD layer in the field) 140 and a pixel cap top plate (or a polysilicon layer) 142 partially overlap. The size of the overlapped area then determines its effective capacitance, which is one of main issues to be improved for a better LCoS performance. According to the cross section of FIG. 2C, the pixel cap bottom plate 140 is separated from the bulk region 144 with a distance 147 approximately equivalent to that of a field oxidation (FOX) 146. This separating distance due to the FOX 146 occupies precious area of the pixel cap bottom plate 140.
For the foregoing reasons, a need has arisen to propose a novel structure and layout of pixel unit cells for effectively improving the effective capacitance of the pixel capacitor and the LCoS performance.